1. Field of the Invention
The present invention relates to a multicast transmission system in which data collected from terminals during calls in multicast transmission is tallied up or compiled and the result of the tallying is distributed, and relates to a data distribution method in such a system.
2. Description of the Related Art
As the multicast transmission system for simultaneously transmitting a message to a plurality of partners, there has been a system using PoC (Push to talk over Cellular) in a mobile communication system. The PoC system is a system that principally uses mobile communication networks and is similar to a walkie-talkie. In the PoC system, a call is made in one-way, i.e., only in one direction.
Also, in the PoC system, like the IM (Instant Messaging) system, call partners can be grouped, and the statuses of the call partners can be observed. Therefore, in the PoC system, the partners in the call status are selected and a call button of a terminal is pushed, thereby enabling a call. In this case, the partner is one person or one group. In other words, the PoC system is similar to the transceiver mode in the mobile telephone. According to the PoC system, it is unnecessary to dial the number of the call destination, a time for connection is short, and the call can be made simultaneously with a plurality of points.
In the PoC system, the calling rate is often set cheaper than the usual call through circuit switching. In the operation procedure, a call destination list prepared in addition to the usual telephone book (i.e., address book) in the mobile telephone is opened, a partner is selected and decided in the call destination list, and then the call is started by pushing the call button. At this time, when a plurality of call destinations are selected, multi-position call is carried out.
Japanese Patent Laid-Open No. 3-289725 (JP, 3-289725A) proposes a technique to prevent the occurrence of data transmission error caused by the interrupt of the voice call and the interruption of the voice call caused by the interrupt of data communication and to prevent switching from the voice call mode to the data communication mode from being forgotten, in a communication system in which data communication and voice communication are performed between a common base station and a plurality of mobile stations. According to this technique, a base station having a data-only radio and a voice-only radio is opposed to a plurality of mobile stations each of which is provided with a data-cum-voice radio. Each mobile station transmits and receives data through a data-only circuit established between the mobile station and the data-only radio in the base station, and transmits and receives voice through a voice-only circuit established between the mobile station and the voice-only radio. The base station is configured to transmit the request data of the voice call to a desirable mobile station by using the data-only circuit. The mobile station is configured to be in the voice call mode, in which the voice-only circuit is used, only for a constant time after the press-to-talk switch is turned ON and to automatically return to the data communication mode, in which the data-only circuit is used, after the constant time elapses, thereby preventing the occurrence of data transmission errors and the interruption of voice call and also preventing the switching from the voice call mode to the data communication mode from being forgotten.
However, in the above-mentioned conventional PoC system, since voices of plural persons cannot be transmitted simultaneously, in order to confirm the intentions of call members while the call is in progress, the intention must be asked while the say is switched one by one, and thus it takes much time until all intentions of members are confirmed. Also, since only voice is multicast-distributed to the group participants, only the voice is communicated among the members. Therefore, expressions and statuses of the participants are hard to be transmitted. In order to confirm whether or not listeners whose faces cannot be viewed from the PTT (Push-To-Talk) speaker actually listen to the speaker's comment, it is necessary to get responses from the listeners.